Thermal deburring apparatus is known; the workpieces to be treated are introduced into a pressure vessel which is filled with a combustible, typically an explosive gas mixture. During combustion, temperatures within the vessel rise to extreme values, in the order of between 2000.degree. to 3000.degree. C. Under such high temperatures, burrs, flashings and other surface areas which are not smooth are combusted, since the relationship of surface area to volume of such burrs, flashings, and the like is high. The workpieces themselves heat only slightly.
The combustion gas usually includes a combustible gas and oxygen, in which oxygen is present in excess. Combustion is initiated by a spark, typically by a spark plug identical or similar to spark plugs customarily used in automotive-type internal combustion engines. It is customary to provide an ignition block which is formed internally with a mixing chamber, in fluid communication with the combustion or treatment chamber itself, on which the spark plug is located, the spark gap itself being introduced into the fluid communication to the combustion chamber. The mixing block, additionally, is used to mix oxygen and the combustion gas.
It has been found that, under some conditions, difficulties arise in igniting the gas mixture. The spark plug may malfunction, or other conditions may prevent proper ignition. For example, ignition can be inhibited by presence of moisture, dampness, or under conditions of poor mixture of the gases introduced into the mixing block and/or the combustion chamber. If the gas/oxygen mixture is not brought to combustion condition, that is, if no explosion results, the workpieces, of course, will not be treated. It is then necessary to vent the chamber, search for the cause of malfunction, and correct it.
Venting the chamber, with the explosive gases therein, must be carried out slowly and carefully; this process is hazardous since the danger of uncontrolled random ignition of the highly explosive gas mixture is always present. Usually, the vessel is vented by a venting valve. The mixing block is contaminated by such venting and residues and contaminants may remain therein, which may later on lead to further damage. The contamination of the mixing chamber is dependent on the size of the vessel, and, hence, of the volume which it includes, and thus of the volume of combustible gas and oxygen which is to be vented.